1. Field of the Invention
The present invention relates to two-component aqueous polyurethane dispersions which have a reduced solvent content and may be cured at ambient temperatures, and to the coatings prepared therefrom which in addition to excellent hardness, flexibility and solvent resistance have improved gloss.
2. Description of the Prior Art
Aqueous polyurethane dispersions and their use for the production of coatings is known. The dispersions may be cured at ambient temperature by evaporation of water and coalescence of the individual particles. These aqueous-based products have been developed in an effort to reduce the amount of organic solvents which are present in corresponding solvent-based coating compositions. Even though the prior art dispersions possess many valuable properties, it has not been possible to obtain coatings which possess all of the properties of coatings obtained from solvent-based coating compositions, especially hardness and solvent resistance, until these objects were achieved in copending application, U.S. Ser. No. 07/559,805, now abandoned.
The copending application relates to two-component coating compositions based on a water dispersible, hydroxy functional polyurethane and a water dispersible polyisocyanate which cure to form coatings with excellent hardness and solvent resistance. One of the disadvantages of these coating compositions is that it is not possible to obtain coatings which have a high gloss unless large amounts of organic cosolvents are added to the dispersions. Since one of the primary reasons for developing aqueous-based coating compositions was to reduce or eliminate the use of organic solvents, the need to add these solvents to obtain coatings which have a high gloss is counter-productive.
Accordingly, it is an object of the subject application to provide coating compositions which do not require large amounts of organic solvents in order to produce high gloss coatings. It is an additional object of the present invention to provide coating compositions which possess all of the advantages of those disclosed in the previously discussed copending application.
These objects may be achieved in accordance with the present invention using low molecular weight polyols as additives for the two-component aqueous coating compositions as described hereinafter.